The present invention relates to a method for manufacturing hypochlorite by electrolyzing brine, and in particular to a method for manufacturing a hypochlorite with available chlorine concentration of 3 to 7 weight % in efficient manner.
The technique to manufacture hypochlorite by electrolyzing brine is widely known in the art. Conventionally, when hypochlorite is manufactured through electrolysis of brine, available chlorine concentration of the hypochlorite thus obtained is mostly as low as 1 weight % or less, while a method to obtain a high concentration hypochlorite having available chlorine concentration of 3 weight % or more through electrolysis is disclosed in JP-A 63-143277. This method is carried out as follows: An aqueous solution with sodium chloride concentration of 10 weight % is electrolyzed without a diaphragm using an anode having a coating of platinum, palladium oxide, ruthenium dioxide and titanium dioxide and a cathode of titanium having area ratio of 1:1.4 to 1:40 to the anode under temperature of 10.degree. to 22.degree. C. and anode current density of 10 to 20 A/dm.sup.2. In this method, titanium having high hydrogen overvoltage is used as cathode, and the cathode has an area smaller than that of the anode to suppress the reduction of hypochlorite ions at the cathode. In this connection, it is disadvantageous in that the current density at cathode is high and cathode voltage is high, thus leading to unfavorable electric power consumption rate. Further, it is also disadvantageous in that oxidizing efficiency of chloride ions by the membrane used as the anode is lower in the regions of high concentration hypochlorite ions.
It is an object of the present invention to provide a method, by which it is possible to solve the problems that electric power consumption rate is low in the manufacture of high concentration hypochlorite by electrolysis as practiced in the past and to manufacture high concentration hypochlorite through electrolysis at low voltage and at high current efficiency.